With the NBA Board of Governors today expected to approve his bid to move the Sonics to Oklahoma City, team owner Clay Bennett’s attorneys already are signaling his strategy for the next big battle: arguing to a federal judge that Seattle’s KeyArena lease lawsuit is just a ruse to force a team sale.

Striking back after a week of bad publicity, Bennett’s attorneys filed a federal-court motion accusing Nickels of a “Machiavellian plan” to force him to sell the Sonics back to Seattle investors led by Microsoft CEO Steve Ballmer.

“This litigation and the recent media frenzy the City helped ignite are part of an agreed-upon strategy between the City and a potential purchaser of the Sonics,” said the motion filed Wednesday.

“That strategy expressly views this litigation as a way to drive up costs for the PBC [Bennett's ownership group, the Professional Basketball Club] — to increase the financial bleeding — to try to force the PBC to sell.”

“He’s got one thing right — the mayor has been working to keep the Sonics in Seattle. The rest of it is a bunch of misrepresentations,” Ceis said.

The Sonics’ filing is the latest volley in the increasingly antagonistic back-and-forth in Seattle’s lawsuit over whether the team should be forced to play out the remainder of its KeyArena lease through September 2010.

In a court filing last week, attorneys for the city revealed embarrassing e-mails in which Bennett and fellow Sonics owners talked enthusiastically about moving the team to Oklahoma City during the one-year period in which the sale agreement pledged “good faith best efforts” to keep the franchise in Seattle.

The Sonics’ latest motion argues Seattle leaders have engaged in their own duplicity — conspiring with Ballmer’s group to ensure that key evidence in the lawsuit remains hidden from public view.

Seattle developer Matt Griffin, part of Ballmer’s group, turned over a stack of documents to Sonics attorneys last week in response to a subpoena. Nearly all the documents were marked “attorney’s eyes only” — meaning they could not be cited publicly in court filings or even shown to Bennett.

The Sonics’ court motion, filed Wednesday by the Seattle law firm of Byrnes & Keller, asks U.S. District Judge Marsha Pechman to order those documents made public.

Among the Griffin documents are spreadsheets and PowerPoint presentations detailing efforts by Ballmer’s group and Seattle to use the lease lawsuit to, as the Sonics motion alleges, “make ‘the Oklahomans’ bleed cash in a hostile media environment.” One e-mail even suggests how much Ballmer might offer for the team, according to the motion.

Other documents show the city knew a $300 million KeyArena renovation Nickels was touting would cost substantially more, the team’s motion alleges.

After first delaying production of the documents, Sonics lawyers argue, Griffin demanded they be designated “attorney’s eyes only” to conceal his group’s scheming with Seattle officials.

Griffin said his group “made a good-faith effort to help KeyArena and help have an NBA team in Seattle,” but referred all questions about the lawsuit to Seattle officials.

Ceis declined to say whether the city would object to disclosure of Griffin’s documents.

Former U.S. Sen. Slade Gorton, who is representing Seattle in its lawsuit, said he had not seen the latest filing.

But Gorton said the Sonics — not the city — started the fight over the KeyArena lease when the team announced it wanted to seek arbitration to escape the lease before it expires in 2010.

He also defended the proposed $300 million KeyArena expansion — toward which Ballmer’s group had offered to contribute $150 million.

“The Ballmer group, before it ever made an offer, made its own independent investigation of the adequacy of the remodel and the cost. It would not have gotten into this business if it had not believed in the validity,” Gorton said.

The Legislature last month declined to act on the proposal, choosing not to authorize King County to raise local taxes for a KeyArena project.

In a written statement Thursday, Nickels blamed Sonics owners for starting the lease fight with the arbitration filing last September. The city’s lawsuit to enforce the lease was filed soon after that.

“The fact is that Mr. Bennett knew the terms of the KeyArena lease when he bought the team, and he was the one who initiated a legal action to break it,” Nickels said.

The city’s federal lawsuit is scheduled for trial in June.

At its meeting today in New York City, the NBA Board of Governors, made up of the league’s 30 team owners, is widely expected to approve the Sonics’ relocation contingent on the outcome of the lease lawsuit.

In anticipation of the team’s arrival, Oklahoma City voters last month approved a $121 million sales-tax package to renovate the city’s Ford Center arena and build an NBA practice facility.

The Oklahoma Legislature sweetened the pot for the NBA Thursday, approving a payroll-tax rebate for the Sonics worth an estimated $60 million over 15 years.

The state House approved the measure 67-32 and sent it to Gov. Brad Henry, who swiftly signed it into law.

“This legislation brings us one step closer to landing an NBA franchise and further confirms that Oklahoma is truly a big league state,” Henry said.